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Interview Questions and Answers - Order By Rating | ||||
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Ans. Yes , but only the read performance in case we don't need to modify it much. In case we need to modify it a lot , it creates write performance overheads as we would need to create many news objects instead of just changing one. | ||||
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Like Discuss Correct / Improve  immutable  immutability objects  immutability | ||||
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Ans. Immutable objects relieves us from the problems of inconsistencies and security and helps with better read performance but at the same time are write performance and storage overheads. In case any modification is required , a new object is created and thus creating multiple copies of it. This is the reason we use StringBuffer / StringBuilder when we have to append some text multiple times and then create a String out of it. | ||||
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Like Discuss Correct / Improve  immutable  immutability objects  immutability | ||||
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This question was recently asked at 'MST Solutions'.This question is still unanswered. Can you please provide an answer. | ||||
Sample Code for composition | ||||
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Like Discuss Correct / Improve  composition  object oriented programming (oops)  oops concepts  oops concepts Asked in 1 Companies basic   frequent | ||||
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Ans. 1. Default definition for some of the methods , like equals, hashcode etc that gets carried to all objects even if you don't define anything. But that default definition is kind of like assigning 0 to integer, it just provide a safe state , nothing much for comparison. 2. Places where you have no idea about what object you may receive and just want to perform out of 8 basic methods of object class, something like printing their string representation ( defined by their toString method ), or equality ( using their equals method ) | ||||
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Like Discuss Correct / Improve  object class | ||||
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Ans. Yes, Runtime Polymprohism requires either Class inheritance or Interface implementation. | ||||
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Like Discuss Correct / Improve  runtime polymorphism  object oriented programming (oops)  oops concepts  method overriding  inheritance  object oriented programming (oops)  oops concepts | ||||
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Ans. We can store the references in a collection by adding to those objects in the collection. We can create a class "ObjectRegistry" with a collection or multiple collections with a search algorithm to look for the already collected objects. | ||||
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Like Discuss Correct / Improve  objects | ||||
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Ans. false false | ||||
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Like Discuss Correct / Improve  object equality  ==  coding  code Asked in 1 Companies | ||||
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Ans. Getting parent class object properties into child class is called Inheritance. The process of representing one form into multiple forms is called polymorphism. | ||||
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Like Discuss Correct / Improve  inheritance  object oriented programming (oops)  oops concepts  polymorphism  object oriented programming (oops)  oops concepts Asked in 1 Companies Basic   frequent | ||||
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Ans. OOPs or Object Oriented Programming is a Programming model which is organized around Objects instead of processes. Instead of a process calling series of processes, this model stresses on communication between objects. Objects that all self sustained, provide security by encapsulating it's members and providing abstracted interfaces over the functions it performs. OOP's facilitate the following features 1. Inheritance for Code Reuse 2. Abstraction for modularity, maintenance and agility 3. Encapsulation for security and protection 4. Polymorphism for flexibility and interfacing | ||||
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Like Discuss Correct / Improve  oops  oops features Asked in 260 Companies basic   frequent | ||||
Very frequently asked. Usually among very first few questions. | ||||
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Ans. Encapsulation is a feature of OOP's that binds the data and it's associated methods together as a single unit and facilitate protection and data hiding by providing minimal interface to outside. For example - member variables are declared private and are accessed through public methods. Moreover we have private methods that can only be used internally and hence providing minimal interface to outside class through use of public methods. | ||||
Sample Code for encapsulation | ||||
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Like Discuss Correct / Improve  encapsulation  object oriented programming (oops)  oops concepts  oops  oops concepts  oops features Asked in 4 Companies Basic   frequent | ||||
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Ans. Java Programs are collection of objects that communicates with each other to get a task accomplished. To add to those objects, there are common spaces ( static i.e common for objects belonging to a class ) that are used too. We can visualize objects as departments of an organization in real world. Just like Task gets initiated in one department and then files are moved across different departments to get work done. In a similar fashion, a task is initiated in one object ( having main method ) and then information ( through POJOs / DTOs ) is moved across objects to accomplish a task. | ||||
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Like Discuss Correct / Improve  objects  Java Programs are collection of objects  real life example of object communication | ||||
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Ans. By encapsulating it within another class and declaring it private. In such a case, it will only be accessible through parent class or parent class object. | ||||
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Like Discuss Correct / Improve  private class   private inner class  class hiding  encapsulation  object oriented programming (oops)  oops concepts  inner classes   nested classes | ||||
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Ans. Private variables are not inherited. They are simply ignored and not made part of the derived object body. | ||||
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Like Discuss Correct / Improve  private variables  inheritance  object oriented programming (oops)  oops concepts | ||||
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Ans. Dynamic dispatch in java is also known as runtime polymorphism.It is a process in which a call to an overriden method is resolved at runtime. | ||||
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Like Discuss Correct / Improve  dynamic dispatch  runtime polymorphism  object oriented programming (oops)  oops concepts | ||||
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Ans. Following Classes in Java SE creates immutable objects String class Wrapper Classes like Integer, Float etc. StackTraceElement Most Enum classes File Class Locale Class | ||||
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Like Discuss Correct / Improve  immutable  immutability objects  immutable  immutability Asked in 1 Companies Basic   frequent | ||||
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Ans. Now the reference points to a new object in memory. If that was the only reference for the previous object , it will be marked for garbage collection. Foe example - Object obj = new Object(); obj = new Object(); object created in first line will be eligible for garbage collection after line 2 as it looses all it's handlers. | ||||
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Like Discuss Correct / Improve  references  objects  garbage collection Asked in 1 Companies | ||||
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Ans. Object is an entity in Java , i.e which has a state ( instance variables ) and methods attached to it ( static or non static , through class definition ). References are the identifiers that are used to point to objects. For example - Employee emp = new Employee(); emp = new Employee(); In this code, emp is the reference that gets assigned to the new object created by the new operator. In the second line , we have assigned the same reference to another object. So with these 2 lines of code, we have 2 objects in memory with reference emp now pointing to second object. | ||||
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Like Discuss Correct / Improve  reference  object  reference vs object Basic   frequent | ||||
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Ans. When it is no longer referenced or it looses all references which were earlier pointing to it. | ||||
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Like Discuss Correct / Improve  garbage collection  object destruction Asked in 1 Companies | ||||
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Ans. We cannot explicitly initiate destruction of an object as no destroy method is available in java. Only Garbage collection can destroy an object. | ||||
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Like Discuss Correct / Improve  Garbage collection  object destruction Asked in 1 Companies | ||||
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Ans. It will print "true" with integers as well as strings. The reason is "Integer constant pool" and "String pool" String pool maintains pool of string literals. When a string literal is used for the first time, a new string object is created and is added to the pool. Upon it's subsequent usage , the reference for the same object is returned. Similarly java uses integer constant pool. | ||||
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Like Discuss Correct / Improve  string pool  object equality  == | ||||
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Ans. dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather than at compile-time. This is used to achieve runtime polymorphism in java. | ||||
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Like Discuss Correct / Improve  overriding  runtime polymorphism  object oriented programming (oops)  oops concepts | ||||
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Ans. Java identifies the method to be called at runtime by the object that is being referenced. | ||||
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Like Discuss Correct / Improve  polymorphism  object oriented programming (oops)  oops concepts  overloading  overriding basic | ||||
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Ans. runtime polymorphism or method overriding doesn't require method name and signature to be different whereas compile time polymorphism or method overloading requires method name to be same but the signature to be different. | ||||
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Like Discuss Correct / Improve  polymorphism  object oriented programming (oops)  oops concepts  overloading  overriding basic | ||||
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Ans. This looks like the case for optimistic locking wherein hibernate suspects that the information in table was updated by some other transaction after the entity was loaded by current transaction. One way is to have synchronized entity state and don't detach the entity. Other could be to merge the entity with the table record rather than just directly persisting the entity. | ||||
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Like Discuss Correct / Improve  StaleObjectStateException  Optimistic locking | ||||
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Ans. Access Control List or ACL is the list of permissions attached to an object in the File System. | ||||
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Like Discuss Correct / Improve  acl  file system  file security  object security  operating system | ||||
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Ans. Composition and Inheritance are the different types of Associations for Classes. Composition is a has-a association between classes. Inheritance is a is-a association between classes. | ||||
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Like Discuss Correct / Improve  composition  object oriented programming (oops)  oops concepts  inheritance  object oriented programming (oops)  oops concepts  association  relationship between objects | ||||
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Ans. 1. Security and Safety - They can be shared across multiple threads as they are thread safe. Moreover, it protects then from bad state due to interception by the other code segment. One such problem due to mutability and access by alternate code segment could be the change of hash code and then the impact on its search with hash collections. 2. Reuse - In some cases they can be reused as only one copy would exist and hence it can be relied upon. For example - String Pool | ||||
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Ans. wait and notify are declared final in object class and hence cannot be overridden. | ||||
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Like Discuss Correct / Improve  object class methods  wait  notify | ||||
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Ans. Class is a template using which objects are created in memory. It's kind of a mold using which objects with body / state are made. | ||||
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Ans. Shallow copy is one of the way for object cloning, other being deep copy. | ||||
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Like Discuss Correct / Improve  cloning  shallow copy  object cloning basic | ||||